1. Field of the Invention
This invention relates to chemical analogs of the sweet glycoside, rebaudioside A, which are themselves sweet and useful as sweeteners and which do not degrade under conditions of use to form physiologically undesirable steviol as does rebaudioside A.
2. The Prior Art
The leaves of the Paraguayan shrub Stevia rebaudiana Bertoni have long been known to be sweet. Several sweet crystalline glycosides have been isolated from these leaves. The principal compound is named stevioside. The secondary compound differs from stevioside in the identity of its saccharide substituent and is known as rebaudioside A. This material has the structure shown in general formula I. ##STR2##
This compound has been identified as a possible sweetener as it provides a relatively sucrose-like intense sweetness. However, it is present in the plant source in small amounts and has not been widely studied.
A threshold question with this material concerns its safety. In 1966, P. V. Vignais and coworkers reported the results of a study concerned with elucidation of the mode of action of the respiratory toxin, atractyligenin. Included in their study were several compounds of related structure including steviol (II), the aglycone of rebaudioside A. ##STR3## Surprisingly, in cell mitochrondria, steviol was found to be an even more potent inhibitor of ATP synthetase then atractyligenin. (Biochim. Biophys. Acta, 118, 465-483 (1966).) In addition, steviol is reported to exhibit antiandrogenic effects (Dorfman, R. I., et al., Endocrinology, 67, 282-285 (1965).) Clearly, if rebaudioside A was converted to steviol in vivo, significant toxicity may be expected. Recent results suggest the likelihood that rebaudioside A would be largely converted to steviol in vivo, and further that the steviol thus produced would subsequently be completely absorbed through the gastrointestinal tract wall. (R. Wingard, J. Dale, J. Brown, R. Hale, F. Enderlin, C. T. Seitz, Experientia, 36, 519, (1980).) Thus, as a result of a combination of the Vignais and Wingard work, it may be concluded that, with widespread use, rebaudioside A may be expected to exhibit significant acute toxicity. If, however, rebaudioside A's metabolism to steviol could be prevented, that is if a potently sweet analog could be developed which was not degraded to steviol, safety for use in foods would be anticipated.